Vulnerability made us human: how our early ancestors turned disability into advantage

June 15, 2015 by David Garner
Reconstruction of Rhodesian Men. Credit: Public Domain

A new evolutionary theory explains how critically small populations of early humans survived, despite an increased chance of hereditary disabilities being passed to offspring.

Anthropologists at the University of York and Newcastle University have studied how our coped during periods when the population dwindled, and have developed a model of early hominins as 'Vulnerable Apes'.

Small numbers of individuals in the distant past would sometimes be driven to landscapes that allowed them to avoid predators and competitors, or exploit emergency resources. They would have become isolated, creating genetic 'bottlenecks' which brought disabling genes to the surface.

The researchers argue that these groups would have experienced a new type of selection pressure – not selection in favour of individuals with the 'best' genes but selection that favoured those who were able to cope with the challenges that their genes threw at them.

They speculate that our need to socialise and ability to experiment and learn new behaviours, as well as our compassion and communication skills, arose as coping strategies that allowed our ancestors to get through these bottlenecks. In so doing, they turned 'disabilities' such as weak jaws, hairless bodies, short, weak arms and straight feet that can't climb trees, into opportunities that formed the platform for future .

Dr Isabelle Winder, from the Department of Archaeology at York, says that this work may change the way anthropologists interpret DNA evidence: "The network pattern of evolution, which has parallels in other groups of animals and plants, has profound implications for DNA studies in anthropology.

"Molecular biologists usually interpret genetic data by assuming a diverging hierarchy and statistically large populations. That may work for bacteria and fruitflies, but the anthropological evidence doesn't line up. Hominin populations were small and lineages seem to have diverged and re-converged in a way that could cause molecular 'clocks' to speed up, slow down and even run backwards."

Dr Nick Winder, from the School of Arts and Cultures, Newcastle University, explains: "This is a new way of thinking about 'fitness'. It wasn't just a matter of having good genes yourself because half your offspring's genes come from someone else. The pool of potential mates would be small and individuals would have to accept the genes on offer or fail to reproduce at all. On some occasions there would be matings between close kin, on others, there would be matings across species boundaries.

"In situations where the probability of producing disabled offspring was high, the 'fittest' individuals would be those that could help their offspring co-exist with this vulnerability. Those that were a little smarter, more flexible, and more compassionate would have been at an advantage."

The researchers suggest that human and non-human primate lineages may have diverged and re-converged many times, and that the conventional 'inverted tree' model of evolution should be replaced with a network of diverging and re-crossing gene-streams.

The study, published in the journal Internet Archaeology, challenges the 'Modern Synthesis' of evolutionary biology which doesn't take hybridisation into account and assumes that populations diverge into reproductively isolated units to create a hierarchy of ever-diverging lineages.

The father and daughter research team is critical of the assumption that the survivors within those populations will be genetically superior to those that disappear, and point to examples of disabled individuals in the archaeological record that could not have survived without communal assistance.

Isabelle says: "Like many other scientists, we believe anthropologists need an 'Extended Synthesis' able to accommodate situations where lineages re-converge, disabling genes may be flushed out of hiding and organisms are capable of social learning that they then turn to their advantage. Our 'Vulnerable Ape' hypothesis could be part of that Extended Synthesis.

"Genetic vulnerability was the trigger that set our ancestors on the path to symbolic language, innovation and pro-social co-operation."

Nick adds: "The reason every new fossil or DNA study seems to force a rethink of human evolution is that biologists are committed to a divergent, hierarchical model, with fierce competition between individual members of large populations.

"The new evidence tends to be much less baffling if you accept that ancient populations were often small and that early hominins had even more complicated sex-lives than our own.

"The traditional competitive model encourages us to think of the relatively high incidence of genetic disability in our species as a threat, but the anthropological evidence suggests that the incidence of genetic disability was probably much higher in the distant past. We have good reason to believe that compassion, ingenuity and behavioural flexibility helped our ancestors cope with this vulnerability."

Nick believes the Vulnerable Ape hypothesis may have implications for the way we cope with threats we face today, such as climate change: "Our earliest ancestors were coping with environmental challenges that drove them through a succession of genetic bottlenecks. Over the last few thousand years, however, innovation has become such a significant driver of evolutionary change in our species that it has entrained planetary life-support systems. We don't yet know how the cognitive skills acquired in tiny communities and refuge-landscapes will serve us on a planet that has few refuge-landscapes left. "

Explore further: In evolution, 'house of cards' model wins

More information: "Complexity, Compassion and Self-Organisation: Human Evolution and the Vulnerable Ape Hypothesis." Internet Archaeology 40. dx.doi.org/10.11141/ia.40.3

Related Stories

In evolution, 'house of cards' model wins

May 14, 2015

Using sophisticated modeling of genomic data from diverse species, Yale researchers have answered a longstanding question about which competing model of evolution works best.

Probing the deep history of human genes and language

January 20, 2015

Brown University evolutionary biologist Sohini Ramachandran has joined with colleagues in publishing a sweeping analysis of genetic and linguistic patterns across the world's populations. Among the findings is that geographic ...

Out of Eurasia, a great primate evolutionary bottleneck?

October 15, 2013

On the road to our modern human lineage, scientists speculate there were many twist and turns, evolutionary dead ends, and population bottlenecks along the way. But how large were population sizes of common ancestors of the ...

The ascent of man: Why our early ancestors took to two feet

May 24, 2013

A new study by archaeologists at the University of York challenges evolutionary theories behind the development of our earliest ancestors from tree dwelling quadrupeds to upright bipeds capable of walking and scrambling.

Recommended for you

Barn owls found to suffer no hearing loss as they age

September 20, 2017

(Phys.org)—A small team of researchers with the University of Oldenburg has found that barn owls do not suffer hearing loss as they get older. In their paper published in Proceedings of the Royal Society B, the group describes ...

Bats anticipate optimal weather conditions

September 20, 2017

Millions of animals fly, swim or walk around the Earth every year. To ensure that they reach their destination, they need to perceive precise changes in environmental conditions and choose the right moment to set off on their ...

5 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

cgsperling
2 / 5 (2) Jun 15, 2015
Interesting. Let's call it the MacGyver model of human evolution.
JVK
1 / 5 (5) Jun 15, 2015
Let's call it what it is: Nutrient-dependent/pheromone-controlled adaptive evolution: a model.
http://www.ncbi.n...24693353

It's another model of how ecological variation leads to ecological adaptations.
Captain Stumpy
5 / 5 (4) Jun 16, 2015
Let's call it what it is: Nutrient-dependent/pheromone-controlled adaptive evolution: a model.
http://www.ncbi.n...24693353

It's another model of how ecological variation leads to ecological adaptations.
@jk
1- it's "another model that uses MUTATIONS"
2- your "model" has been debunked using actual biology and experimental evidence as well as known validated data: see here
http://www.socioa...ew/24367

so let's not even call it anything except what it is: A model of creationist origins & ideals which use mutations, but can't stomach the word so instead tries to buffalo a reader with large techno-verbiage which means "mutations", but then ignores that the actual science that does work in the "model" simply supports EVOLUTION theory and it's experimental evidence anyway

be like Cantdrive! Call a Duck a Birkeland current!
mapmanic
4 / 5 (4) Jun 20, 2015
I don't buy it. We don't have to look far into the dim past to test this hypothesis -- we can look at the genetics of small isolated bands in the Amazon, for example. Faulty recessive genes can hide in large populations with only the rare homozygous pairing causing the defect to be expressed, but in small inbred groups these genes tend to be eliminated faster since they are more likely to be expressed. Relaxation of selection would more easily explain the existence of "broken" genes. So perhaps the authors of the study have reversed cause and effect.
Torbjorn_Larsson_OM
5 / 5 (1) Jun 21, 2015
Looks to be poor science since they reject well tested genetics, especially the usual senses of molecular clocks (who can't "run backwards" anymore than other clocks), fitness and kin selection, and reinterprets it as group selection - which has never been observed. Also, they don't predict how Neanderthals could retain a more robust phenotype, despite having lived longer in the "small group" mode. Instead mapmanic has what happens correctly, I think.

Looks like a major fail, and it is easy to predict nothing will come out of it.

@Ren: What is strange is trolls like you. What use are they, and what brains do they have, trying to trash talk existing science (which never, ever use "miracles" - try to find a reference claiming it!)? Not much.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.